The present invention relates to medical electrical leads generally, and more particularly to implantable defibrillation electrodes and leads.
Early concepts of implantable defibrillators, such as disclosed in U.S. Pat. Re. No. 27,652 by Mirowski et al., envision an electrode system employing a ventricular endocardial electrode and a plate electrode mounted to the heart directly, subcutaneously, or to the skin. However, it has long been recognized that a totally transvenous system would be desirable to simplify the use of implantable defibrillators. One such system is suggested in U.S. Pat. No. 3,942,536 by Mirowski et al., which discloses a transvenous lead having electrodes intended for location in the right ventricular apex and in the superior vena cava. Such systems were eventually tested in human beings, with some success. However, currently available implantable defibrillators typically employ epicardial patch electrodes, alone, or in conjunction with transvenous electrodes.
While systems employing epicardial patch electrodes are workable, a thoracotomy is required to apply the epicardial electrodes. It is generally believed that it would be desirable to produce an implantable defibrillation system which entirely avoids the necessity of a thoracotomy, and there has been substantial work directed toward development of such systems, as disclosed in U.S. Pat. No. 4,727,877 issued to Kallok, U.S. Pat. No. 4,708,145 issued to Tacker et al. and as disclosed in U.S. application Ser. No. 07/284,957 filed Dec. 15, 1988 by Mehra, for an "Endocardial Defibrillation Electrode System". Other endocardial defibrillation electrodes are disclosed in U.S. Pat. No. 4,481,953 issued to Gold et al., U.S. Pat. No. 4,161,952 issued to Kinney et al., U.S. Pat. No. 4,934,049 issued to Kiekhafer et al. and in U.S. patent application Ser. No. 07/479,928, filed Feb. 14, 1990 by Holleman et al., for an "Implantable Electrode and Method for Fabrication". The Kinney, Gold, and Kiekhafer patents and the Holleman et al. application all disclose endocardial defibrillation leads employing defibrillation electrodes fabricated from elongated coils of biocompatible metal, mounted exposed to the exterior of the defibrillation lead, for location in the right ventricle and other locations within the heart. U.S. Pat. No. 4,641,656 issued to Smits and the above cited Mehra application both disclose a variety of endocardial defibrillation electrodes intended for use in the atrium, ventricle, and coronary sinus, all of which employ electrodes taking the form of elongated coils of conductive biocompatible metals.
Recently, it has been recognized that increasing the surface area of defibrillation electrodes located in the right ventricle may be one way to provide reduced defibrillation thresholds. U.S. Pat. No. 5,144,960 issued to Mehra et al. accomplishes an increased surface area by means of a bifurcated lead having two elongated electrode coils located in the right ventricle. U.S. Pat. No. 5,010,894 issued to Edhag also discloses right ventricular defibrillation leads having multiple electrode coils having differing configurations. U.S. Pat. No. 5,133,365 discloses a right ventricular defibrillation lead having a spiral configuration and U.S. Pat. No. 5,007,436 discloses a right ventricular lead having a J-shaped configuration.